1. Field of the Invention
The present invention relates generally to facilitating release of powder contained in a receptacle. More specifically, the present invention relates to the administration of medication by a method and apparatus for facilitating inhalation of powder medicaments.
2. Related Art
In the medical field, it is often desirable to administer various forms of medication to patients. Well known methods of introducing medication into the human body include the oral ingestion of capsules and tablets, intravenous injection through hypodermic needles, and numerous others. In one method, certain medications may be inhaled into a patient's respiratory tract and lungs through the nose or mouth. Certain of these medications, such as bronchodilators, corticosteroids, etc., for the treatment of asthma and other respiratory anomalies, may be aimed at the respiratory tract directly. Others are inhaled for purposes of systemic treatment, i.e. for treatment of any area of the body through absorption from the respiratory tract through the lung tissue, into the deep lungs, and into the bloodstream. Each of these medications comes in a variety of forms, including fluids, which are commonly administered as an aerosol vapor or mist, as well as solids. Inhalable solids typically take the form of fine, dry powders. Specialized devices, such as inhalers, are provided to assist the patient in directing these fine powder medications into the respiratory tract.
Various types of inhalers are known for the administration of dry powder medicaments. However, each of these inhalers suffers certain drawbacks. For example, U.S. Pat. No. 5,787,881 discloses an inhaler that is used with encapsulated dry powder medicaments. However, use of this device requires numerous steps and imposes a number of inconveniences on a user. For example, the medication capsules used with the device have an aperture formed therein prior to insertion into an opening in the inhaler. Therefore, there exists a danger that an amount of medication may be lost prior to or during insertion into the device. After insertion of the capsule, use of the device requires the additional step that a cover must be closed before the medication may be inhaled.
Inhalation devices configured for use with a capsule containing some type of medicament are shown in U.S. Pat. No. 4,069,819 to Valentini et al. (“the '819 patent”) and U.S. Pat. No. 4,995,385 to Valentini et al. (“the '385 patent”). The inhalation device described in the '385 patent was developed to overcome the drawbacks of the device described in the '819 patent. Particularly, in a large number of cases, the device described in the '819 patent experienced irregular and incomplete emptying of the capsule, thereby resulting in difficulties in properly administering the medicament in the capsule. The inhalation device described in the '385 patent attempts to overcome this deficiency by tapering the nebulization chamber toward the end surface that comprises the discharge holes. Thus, the nebulization chamber of the '385 patent is not cylindrical, but rather frusto-conical in form in an attempt to achieve regular complete emptying of the nebulization chamber.
However, further improvements in the design of inhalation devices are needed to achieve high emitted doses and highly dispersed powders while maintaining low resistance, especially when the inhaler is used with high doses and is operated at low peak inspiratory flow rates (PIFR) and low inhalation volumes. As used herein, “emitted dose” (ED) refers to the percentage of the dose of powder medicament that is emitted from a receptacle in the inhalation device. The dispersal of the powder can be quantified by measuring the volume mean geometric diameter (VMGD) of the emitted powder. As used herein “volume mean geometric diameter” refers to the average geometric diameter of the powder. As used herein, “resistance” refers to the square root of the pressure gradient across the inhaler divided by the peak inspiratory flow rate through the inhaler. As used herein “low peak inspiratory flow rate” refers to a peak inspiratory flow rate of approximately 25 L/min or less. Moreover, improvements are needed to achieve high emitted doses and highly dispersed powders that are consistently reproducible, i.e., that have a low standard deviation of emitted dose percentage and VMGD, respectively.
Another drawback of the inhalation devices described in the '819 and the '385 patents is the piercing device that is used to puncture the capsule. Such conventional piercing devices are formed from circular stock, with the points created by pinching the stock at an angle, thereby creating a single sharp cutting edge. Drawbacks of such a design are that the point (which must puncture the capsule material) is often rounded, lessening its effectiveness as a piercing device. Moreover, burrs often form on the lower edge, which can stop the piercing device from retracting from the capsule, thereby causing a device failure. The holes formed by such a conventional piercing device are generally round, and do not have the appearance of being cut by a sharp edge. With such a conventional design, the capsule is often crushed, rather than punctured or pierced. If such a conventional piercing device is used with brittle capsule materials such as gelatin, pieces of capsule material of a size that can be inhaled are usually broken off from the capsule. Thus, conventional piercing devices are less than optimal, particularly for brittle capsule material.
Another drawback of conventional inhalation devices is that they have no means for indicating when the powder in the inhaler is ready for inhalation by the user. It is desirable to have a means for indicating to the user that a dose of powder is ready for inhalation. For example, it would be desirable for a patient using a device for dispensing fluticasone propionate (used to treat asthma) to know when the device is ready for inhalation.
Thus, there is a need in the art for an improved method and apparatus for inhalation of dry powder medicaments. What is needed is an inhaler that provides for a higher emitted dose that is consistently reproducible with low standard deviation. Such a need is particularly acute for low peak inspiratory flow rates, and for high dosage ranges. There is a further need in the art for an improved means for puncturing the capsule containing the medicament. The present invention, the description of which is fully set forth below, solves the need in the art for such improved methods and apparatus.